1. Field of the Invention
The present invention relates to a method and an apparatus for grinding a cylindrical workpiece and, more particularly, to a method and an apparatus for grinding a cylindrical surface of a workpiece by traverse grinding.
2. Discussion of the Prior Art
Conventionally, when the axial length of a cylindrical surface of a workpiece is longer than the width of a grinding wheel, the cylindrical surface is ground by traverse grinding. In such traverse grinding, the grinding wheel is firstly advanced toward the rotational axis of a workpiece to carry out infeed movement into the cylindrical surface thereof, and a table supporting the workpiece is then moved in a direction parallel to the rotational axis of the workpiece so that the whole area of the cylindrical surface of the workpiece is ground by the grinding wheel.
Further, when it is required to ground a cylindrical surface of a workpiece at a high speed, so-called one-path traverse grinding is used for grinding the cylindrical surface, wherein the cylindrical surface is ground into a desired final dimension by a single traverse movement of the grinding wheel under the state that a large depth of cut has been given.
Such high speed traverse grinding, however has a problem that one end la of the workpiece 1 at which traverse grinding ends is excessively ground as compared to the rest of the cylindrical surface of the workpiece 1, as shown in FIG. 1. This causes a deterioration of the cylindricity of the outer surface.
The excessive removal at the end la is caused by a change in the grinding force during such traverse grinding. Namely, the grinding force is decreased when the grinding wheel approaches the end la of the workpiece 1, because the width b of an effective part of the grinding surface which actually carries out the grinding function decreases, as shown in FIGS. 2(i a) and 2(b). For example, when the width of the effective part of the grinding surface becomes the half of the width of the grinding surface B, the grinding force also becomes half. This decrease of the grinding force causes an increase of the grinding efficiency, and an decrease of the deformation amount in the radial direction of the workpiece 1, resulting in an excessive grinding at the end of the cylindrical surface.